Abstract:

A pressure relief valve includes a valve body having a valve seat fluidly
positioned between an inlet and an outlet. A valve member is movable
among a first position, a second position, and a third position. The
valve member is in contact with the valve seat and fluidly blocks the
inlet from the outlet at the first position. At the second position of
the valve member, the inlet is fluidly connected to the outlet via a
small flow area. The inlet is fluidly connected to the outlet via a large
flow area when the valve member is at the third position. An electrical
actuator is attached to the valve body and is operably coupled to move
the valve member when energized. The valve member includes an opening
hydraulic surface exposed to fluid pressure in the inlet when at the
first position. A spring is operably positioned to bias the valve member
toward the second position when the valve member is at the third
position.

Claims:

1. A pressure relief valve, comprising:a valve body having a valve seat
fluidly positioned between an inlet and an outlet;a valve member being
movable among a first position, a second position, and a third
position;the valve member being in contact with the valve seat and
fluidly blocking the inlet from the outlet at the first position;the
inlet being fluidly connected to the outlet via a small flow area when
the valve member is at the second position;the inlet being fluidly
connected to the outlet via a large flow area when the valve member is at
the third position;an electrical actuator attached to the valve body and
being operably coupled to move the valve member when energized;the valve
member having an opening hydraulic surface exposed to fluid pressure in
the inlet when at the first position; anda first spring operably
positioned to bias the valve member toward the second position when the
valve member is at the third position.

2. The pressure relief valve of claim 1, wherein the electrical actuator
is a solenoid with an armature coupled to move the valve member toward
one of the first position and the second position when the solenoid is
energized.

3. The pressure relief valve of claim 2, further including a second spring
operably positioned to bias the valve member toward one of the first
position and the second position.

4. The pressure relief valve of claim 3, wherein the weak spring biases
the valve member toward the second position.

5. The pressure relief valve of claim 3, wherein the weak spring biases
the valve member toward the first position.

6. The pressure relief valve of claim 2, wherein the third position of the
valve member includes an overtravel position of the armature.

7. An engine system, comprising:a low static leak fuel system that
includes:a common rail;a plurality of fuel injectors fluidly connected to
the common rail via individual branch passages;a variable delivery
high-pressure pump with an outlet fluidly connected to an inlet of the
common rail;a fuel tank;a fuel transfer pump with an inlet fluidly
connected to the fuel tank, and an outlet fluidly connected to an inlet
of the variable delivery high-pressure pump;a pressure relief subsystem
including an electrical actuator, and the pressure relief subsystem
having a first configuration, a second configuration, and a third
configuration, and fluid communication between the common rail and the
fuel tank being closed in the first configuration, and the common rail
being in fluid communication with the fuel tank via a small flow area in
the second configuration, and the common rail being in fluid
communication with the fuel tank via a large flow area in the third
configuration, and the pressure relief subsystem being hydraulically
moved from the first configuration to the third configuration responsive
to fluid pressure in the common rail exceeding a predetermined pressure
that is greater than a predetermined maximum operating pressure of the
fuel system; andan electronic controller in individual control
communication with each of the pressure relief subsystem, the variable
delivery high-pressure pump and the plurality of fuel injectors, and the
electronic controller being configured to communicate a pressure decay
control signal to the electrical actuator to move the pressure relief
subsystem from the first configuration to the second configuration and
then back to the first configuration responsive to an engine load
reduction determination.

8. The engine system of claim 7, wherein the pressure relief subsystem
includes a valve with a valve member at a first position in contact with
a valve seat in the first configuration, at a second position out of
contact with the valve seat in the second configuration, and at a third
position further out of contact with the valve seat in the third
configuration.

9. The engine system of claim 8, wherein the valve includes:a first spring
positioned to bias the valve member toward one of the first position and
the second position; anda second spring positioned to bias the valve
member toward the second position when the valve member is at the third
position.

10. The engine system of claim 9, wherein the electronic controller is
configured to communicate a pressure overshoot control signal to the
electrical actuator to move the valve member from the first position to
the second position and then back to the first position responsive to an
engine load increase determination.

11. The engine system of claim 10, wherein the electronic controller is
configured to communicate a depressurization control signal to the
electrical actuator to move the valve member from the first position to
the second position responsive to an engine off determination.

12. The engine system of claim 11, wherein the electronic controller is
configured to communicate a parasitic loss control signal to the
electrical actuator to move the valve member from the first position to
the second position responsive to an engine low load determination.

13. The engine system of claim 12, wherein the valve member is biased by
at least one of the first spring and the second spring toward the first
position when the electrical actuator is de-energized.

14. The engine system of claim 12, wherein the valve member is biased by
at least one of the first spring and the second spring toward the second
position when the electrical actuator is de-energized.

15. A method of operating an engine having a low static leak fuel system,
comprising the steps of:supplying fuel to a common rail by operating a
variable delivery high-pressure pump;supplying fuel from the common rail
to a plurality of fuel injectors via individual branch passages;injecting
fuel from the plurality of fuel injectors directly into respective engine
cylinders;igniting the fuel in the respective engine cylinders;
andtransitioning from a first high engine load to a first low engine
load, the transitioning step including opening and then closing a fluid
connection between the common rail and a fuel tank.

16. The method of claim 15, including the step of transitioning from a
second low engine load to a second high engine load, the second
transitioning step including opening and then closing the fluid
connection between the common rail and a fuel tank.

17. The method of claim 16, including the steps of:stopping the engine;
andopening and then closing the fluid connection between the common rail
and a fuel tank after stopping the engine.

18. The method of claim 17, including the steps of:reducing torque
reversals in a gear train powering the variable delivery high-pressure
pump by pumping fuel to the common rail in excess of a combined fuel
injection quantity of the plurality of fuel injectors; andreturning the
excess fuel to the fuel tank by opening the fluid connection between the
common rail and the fuel tank.

19. The method of claim 18, wherein the opening steps are accomplished by
one of energizing and de-energizing an electrical actuator of a valve.

20. The method of claim 19, wherein each of the opening steps
includes:opening a small flow area fluid connection between the common
rail and the fuel tank;exceeding a predetermined maximum operating
pressure in the common rail; andopening a large flow area fluid
connection with the valve to reduce pressure in the common rail below the
predetermined maximum operating pressure.

Description:

TECHNICAL FIELD

[0001]The present disclosure relates generally to pressure control in
common rail fuel systems, and more particularly to a means for
controlling rail pressure in low static leak fuel systems.

BACKGROUND

[0002]Common rail fuel systems typically include a fuel source and fuel
delivery components for supplying fuel directly into cylinders of an
internal combustion engine by way of a common rail. Fuel within the
common rail may be pressurized to a relatively high pressure using one or
more pumps, and may be delivered to fuel injectors through a plurality of
individual fuel supply passages. A control system may be associated with
the fuel system to monitor and control operation of one or more of the
fuel system components. Specifically, for example, the control system may
be configured to control the high-pressure pump and each of the fuel
injectors to control pressurization rates and injection, thus improving
performance and control of the engine. Typically, such fuel systems also
include some means to protect the system against gross
over-pressurization, which may occur due to one or more of an
operational, control, or component problem. Often, this protection is
provided through the use of a pressure relief valve, which may be
mechanically or electronically actuated when rail pressure is above a
predetermined maximum operating pressure.

[0003]Engineers are constantly seeking improved performance and expanded
capabilities for such fuel systems. For example, a low static leak fuel
system may provide minimal leakage and, as a result, may improve the
overall efficiency, reliability, and durability of common rail fuel
systems. However, the lack of static leakage from the fuel system may
present a previously unrecognized performance challenge, such that when a
reduction in rail pressure is required, the pressure may not be reduced
at a desired rate. More specifically, conventionally designed fuel
systems, which may allow a tolerable amount of leakage, may increase a
reduction rate, or decay rate, of pressure within the rail, whereas the
low static leak fuel system may not. As a result, for example, the settle
time required for an operational engine having a low static leak fuel
system to go from a high load condition, during which relatively high
rail pressures are used, to a low load or idle condition, during which
relatively low rail pressures are used, may be compromised.

[0004]As introduced above, a variety of mechanical and electronic means
for preventing over-pressurization within common rail fuel systems are
generally known. For example, U.S. Pat. No. 7,392,792 teaches a pressure
relief valve that may fluidly connect the common rail to the fuel tank
via a fluid passageway to relieve pressure from the fuel system. Although
the commonly owned reference is directed to a method for dynamically
detecting fuel leakage, a pressure relief valve that may be actuated when
rail pressure exceeds a biasing spring force and/or when a solenoid is
energized is described. While the reference may effectively reduce or
prevent over-pressurization from occurring, it does not recognize a need
for controlling rail pressure in low static leak fuel systems.

[0005]The present disclosure is directed to one or more of the problems
set forth above.

SUMMARY OF THE DISCLOSURE

[0006]In one aspect, a pressure relief valve includes a valve body having
a valve seat fluidly positioned between an inlet and an outlet. A valve
member is movable among a first position, a second position, and a thud
position. The valve member is in contact with the valve seat and fluidly
blocks the inlet from the outlet at the first position. At the second
position of the valve member, the inlet is fluidly connected to the
outlet via a small flow area. The inlet is fluidly connected to the
outlet via a large flow area when the valve member is at the third
position. An electrical actuator is attached to the valve body and is
operably coupled to move the valve member when energized. The valve
member includes an opening hydraulic surface exposed to fluid pressure in
the inlet when at the first position. A first spring is operably
positioned to bias the valve member toward the second position when the
valve member is at the third position.

[0007]In another aspect, an engine system includes a low static leak fuel
system. The low static leak fuel system includes a common rail and a
plurality of fuel injectors fluidly connected to the common rail via
individual branch passages. A variable delivery high-pressure pump
includes an outlet fluidly connected to an inlet of the common rail. The
low static leak fuel system also includes a fuel tank and a fuel transfer
pump having an inlet fluidly connected to the fuel tank and an outlet
fluidly connected to an inlet of the variable delivery high-pressure
pump. A pressure relief subsystem includes an electrical actuator and has
a first configuration, a second configuration, and a third configuration.
In the first configuration, fluid communication between the common rail
and the fuel tank is closed. In the second configuration, the common rail
is in fluid communication with the fuel tank via a small flow area. In
the third configuration, the common rail is in fluid communication with
the fuel tank via a large flow area. The pressure relief subsystem is
hydraulically moved from the first configuration to the third
configuration in response to fluid pressure in the common rail exceeding
a predetermined pressure that is greater than a predetermined maximum
operating pressure of the fuel system. An electronic controller is in
individual control communication with each of the pressure relief
subsystem, the variable delivery high pressure pump, and the plurality of
fuel injectors, and is configured to communicate a pressure decay control
signal to the electrical actuator to move the pressure relief subsystem
from the first configuration to the second configuration and then back to
the first configuration in response to an engine load reduction
determination.

[0008]In yet another aspect, a method of operating an engine having a low
static leak fuel system includes supplying fuel to a common rail by
operating a variable delivery high-pressure pump. Fuel is supplied from
the common rail to a plurality of fuel injectors via individual branch
passages. Fuel is injected from the plurality of fuel injectors directly
into respective engine cylinders, and is ignited within the respective
engine cylinders. The engine is transitioned from a first high engine
load to a first low engine load. This transitioning step including
opening and then closing a fluid connection between the common rail and a
fuel tank.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a schematic view of an engine system, which includes a low
static leak fuel system, according to one aspect of the present
disclosure;

[0010]FIG. 2 is a sectioned view through a two-stage pressure relief valve
for use with the engine system of FIG. 1, the two-stage pressure relief
valve being shown in a first configuration;

[0011]FIG. 3 is a sectioned view of the two-stage pressure relief valve of
FIG. 2, the two-stage pressure relief valve being shown in a second
configuration;

[0012]FIG. 4 is a sectioned view of the two-stage pressure relief valve of
FIG. 2, the two-stage pressure relief valve being shown in a third
configuration;

[0013]FIG. 5 is a sectioned view through an alternative embodiment of the
two-stage pressure relief valve depicted in FIGS. 2-4;

[0014]FIG. 6 is a sectioned view through an alternative embodiment of a
two-stage pressure relief valve for use with the engine system of FIG. 1;

[0015]FIG. 7 is a sectioned view through another alternative embodiment of
a two-stage pressure relief valve for use with the engine system of FIG.
1;

[0016]FIG. 8 is a sectioned view through yet an alternative embodiment of
a two-stage pressure relief valve for use with the engine system of FIG.
1; and

[0017]FIGS. 9a-9d are graphs of actuator voltage, valve position, flow
area schedule, and rail pressure versus time for an exemplary engine
operation, according to one embodiment of the present disclosure.

DETAILED DESCRIPTION

[0018]Referring to FIG. 1, an engine system 10 may generally include an
internal combustion engine 12, such as a compression ignition engine. The
internal combustion engine 12 may include an engine block 14 that defines
a plurality of cylinders 16, each of which forms a combustion chamber 18.
A piston 20 is slidable within each cylinder 16 to compress air within
the respective combustion chamber 18. The internal combustion engine 10
also includes a crankshaft 22 that is rotatably disposed within the
engine block 14. A connecting rod 24 may connect each piston 20 with the
crankshaft 22 such that sliding motion of the pistons 20 within each
respective cylinder 16 results in a rotation of the crankshaft 22.
Similarly, rotation of the crankshaft 22 may result in linear sliding
motion of the pistons 20.

[0019]The engine system 10 may also include a low static leak fuel system
26, also referred to as a common rail fuel system, for supplying fuel
into each of the combustion chambers 18 dining operation of the internal
combustion engine 12. The low static leak fuel system 26, as described
herein, may be characterized as such based on a pressure decay from a
predetermined maximum operating pressure to a predetermined minimum
operating pressure in a particular time. For example, the low static leak
fuel system 26 may include a fuel system that transitions from the
maximum operating pressure to the minimum operating pressure in greater
than about two seconds. As should be appreciated, fuel systems that
transition from maximum operating pressure to minimum operating pressure
in less than about two seconds may not generally be characterized as
exhibiting low static leakage.

[0020]The low static leak fuel system 26 may include a fuel tank 28
configured to hold a supply of fuel, and a fuel pumping arrangement 30
configured to pressurize the fuel and direct the pressurized fuel to a
plurality of fuel injectors 32 by way of a common rail 34. The fuel
pumping arrangement 30 may include one or more pumping devices that
function to increase the pressure of the fuel and direct one or more
pressurized streams of fuel to the common rail 34 using fuel lines 36.
For example, the fuel pumping arrangement 30 may include a fuel transfer
pump 38 having an inlet 38a fluidly connected to the fuel tank 28, and an
outlet 38b fluidly connected to an inlet 40a of a variable delivery
high-pressure pump 40. The variable delivery high-pressure pump 40, which
may increase the pressure of the fuel to a range of about 30-300 MPa, may
have an outlet 40b that is fluidly connected to an inlet 34a of the
common rail 34. One or both of the fuel transfer pump 38 and the variable
delivery high-pressure pump 40 may be operably connected to the internal
combustion engine 12 and driven by the crankshaft 22. For example, the
variable delivery high-pressure pump 40 may be connected to the
crankshaft 22 through a gear train 42.

[0021]The fuel injectors 32 may be disposed within a portion of the
cylinder block 14, as shown, and may be connected to the common rail 34
via a plurality of individual branch passages 44. Each fuel injector 32
may be operable to inject an amount of pressurized fuel into an
associated combustion chamber 18 at predetermined timings, fuel
pressures, and fuel flow rates. The timing of fuel injection into the
combustion chambers 18 may be synchronized with the motion of the pistons
20. For example, fuel may be injected as piston 20 nears a
top-dead-center position in a compression stroke to allow for
compression-ignited combustion of the injected fuel. Alternatively, fuel
may be injected as piston 20 begins the compression stroke heading
towards a top-dead-center position for homogenous charge compression
ignition operation. As shown, fuel injectors 32 may also be fluidly
connected to fuel tank 28 via one or more drain lines 45.

[0022]A control system 46 may be associated with low static leak fuel
system 26 and/or engine system 10 to monitor and control the operations
of the fuel pumping arrangement 30, fuel injectors 32, and various other
components of the fuel system 26. In particular, and according to the
exemplary embodiment, the control system 46 may include an electronic
controller 48 in communication with the variable delivery high-pressure
pump 40 and each of the fuel injectors 32 via communication lines 50. For
example, the electronic controller 48 may be configured to control
pressurization rates and injection, thus improving performance and
control of the internal combustion engine 12. Although a particular
embodiment is shown, it should be appreciated that the control system 46
may be configured to provide any desired level of control, and may
include any number of components and/or devices, such as, for example,
sensors, useful in providing the desired control.

[0023]The electronic controller 48 may be of standard design and may
generally include a processor, such as for example a central processing
unit, a memory, and an input/output circuit that facilitates
communication internal and external to the electronic controller 48. The
central processing unit may control operation of the electronic
controller 48 by executing operating instructions, such as, for example,
programming code stored in memory, wherein operations may be initiated
internally or externally to the electronic controller 48. A control
scheme may be utilized that monitors outputs of systems or devices, such
as, for example, sensors, actuators or control units, via the
input/output circuit to control inputs to various other systems or
devices. For instance, the electronic controller 48 may be in control
communication with each of the fuel injectors 32 or, more specifically,
actuators thereof via communication lines 50 to deliver the required
amount of fuel at the correct time. Further, the electronic controller 48
may communicate control signals to variable delivery high-pressure pump
40 via communication lines 50 to control pressure and output of the
high-pressure pump 40 to common rail 34.

[0024]The engine system 10 or, more particularly, the low static leak fuel
system 26 may also include a pressure relief subsystem 52. The pressure
relief subsystem 52, generally speaking, may include a means for opening
and closing a fluid connection between the common rail 34 and the fuel
tank 28, or other drain. According to one embodiment, the pressure relief
subsystem 52 may include a two-stage pressure relief valve 54, which may
receive electronic control signals from electronic controller 48. The
two-stage pressure relief valve 54, shown in a first configuration in
FIG. 2, may generally include a valve body 70 having a valve seat 72
fluidly positioned between an inlet 74, which may be fluidly connected
with the common rail 34, and an outlet 76, which may be fluidly connected
to the fuel tank 28 via drain lines 45. A valve member 78 may be movable,
relative to the valve seat 72, among a plurality of positions, including
a first position, which is shown. Specifically, at the first position,
the valve member 78 may be in contact with the valve seat 72 and,
therefore, may fluidly block the inlet 74 from the outlet 76.

[0025]According to one embodiment, an electrical actuator 80 may be
attached to the valve body 70 and operably coupled to move the valve
member 78 when energized. The electrical actuator 80 may include a
solenoid 84 with an armature 86 that is coupled to move the valve member
78 toward the first position when the solenoid 84 is energized.
Specifically, the solenoid 84 may be energized to move valve member 78
into the first position against a spring force provided by a second
spring 88, which may be considered a weak spring relative to a first
spring 92. Alternatively, or additionally, the solenoid 84 may be
energized to urge the valve member 78 against an opening force acting on
an opening hydraulic surface 90 of the valve member 78. Further, such
movement may effectively decouple the valve member 78 from a first spring
92, which may be considered a strong spring relative to second or weak
spring 88, and is discussed later in greater detail. Although the
electrical actuator 80 is depicted as including a solenoid 84 and
armature 86, it should be appreciated that the electrical actuator 80 may
include any of a variety of known actuators. For example, the electrical
actuator 80 may include a piezo electrical actuator having a piezo stack
that changes in length in response to control signals, or voltages,
received on communication lines 50 from electronic controller 48.

[0026]Turning now to FIG. 3, the two-stage pressure relief valve 54 is
shown in a second configuration. In the second configuration, the
electrical actuator 80 may be de-energized, thus allowing the weak spring
88 to bias the valve member 78 into a second, or slightly opened,
position. Specifically, the weak spring 88 may urge the valve member 78
out of contact with the valve seat 72. Further, fluid pressure in the
common rail 34 acting on opening hydraulic surface 90 may urge valve
member 78 toward the second position. As a result, the inlet 74 of the
two-stage pressure relief valve 54 may be fluidly connected to the outlet
76 of the valve 54 via a small flow area, as shown. In addition, the
valve member 78 may be effectively coupled with the strong spring 92 in
the second configuration of the two-stage pressure relief valve 54. It
should be appreciated that the strong spring 92 may only be characterized
as "strong" relative to the weak spring 88. Specifically, the strong
spring 92 may include a greater pre-load than the weak spring 88.
Similarly, the weak spring 88 may be considered "weak" only with respect
to the strong spring 92.

[0027]A third configuration of the two-stage pressure relief valve 54 is
shown generally in FIG. 4. In the third configuration of the two-stage
pressure relief valve 54, the inlet 74 may be fluidly connected to the
outlet 76 via a large flow area, as shown. More specifically, the
electrical actuator 80 may be de-energized, allowing a predetermined
fluid pressure level within the common rail 34 to urge the valve member
78 upward and into a third position, against a predetermined pre-load of
strong spring 92. It should be appreciated that, in the thud position,
the valve member 78 may be further out of contact with the valve seat 72
than it is in the second position and, as a result, the flow area
provided in the third configuration of the two-stage pressure relief
valve 54 may be greater than that provided in the second configuration.
According to one embodiment, the two-stage pressure relief valve 54 may
be configured to allow movement of the valve member 78 into the thud
position when fluid pressure in the common rail 34 exceeds a
predetermined pressure that is greater than a predetermined maximum
operating pressure of the low static leak fuel system 26.

[0028]Alternatively, as shown in FIG. 5, a two-stage pressure relief valve
100 for use with the present disclosure may be provided with only one
spring 102. Specifically, the two-stage pressure relief valve 100 may be
similar to the two-stage pressure relief valve 54 of FIGS. 2-4, but may
be biased to a slightly open position in response to pressure within the
common rail 34, rather than in response to a spring load. When electrical
actuator 104 is de-energized, valve member 106 may be moved out of
contact with valve seat 108 and into a moderate flow position, which may
be similar to the second position described above. This moderate flow
position, which may allow flow through a first outlet 110, may be
configured to provide damping of significant rail pressure changes, while
allowing the common rail 34 to build and maintain sufficient rail
pressure. As rail pressure increases, such as above a predetermined
maximum operating pressure, valve member 106 may be moved further upward,
against a spring force provided by spring 102 and into a third position,
to allow pressure relief through a second outlet 112.

[0029]It should be appreciated that the pressure relief subsystem 54 may
include a number of additional or alternative valve configurations,
without deviating from the scope of the present disclosure. Although
"leaking" pressure relief valves have been shown in FIGS. 2-5, pressure
relief valves that are biased to a closed, or "non-leaking," position may
also be used. For example, as shown in FIG. 6, the pressure relief
subsystem 52 may include an alternative two-stage pressure relief valve
120. According to the alternative embodiment, a spring 122 and/or
armature pin 124 may bias valve member 126 toward the first, or closed,
position. An electrical actuator 128 may be energized to move armature
pin 124 slightly upward, thus allowing rail pressure to move valve member
126 into the second position. An overtravel mechanism 130 may allow the
armature pin 124 to assume an overtravel position when the valve member
126 is moved into the third position. Specifically, when rail pressure
increases above a predetermined maximum operating pressure, valve member
126 may be moved upward, against a predetermined preload of spring 122,
thus moving armature pin 124 against a spring 132 positioned within a
solenoid spring bore 134.

[0030]As should be appreciated, the overtravel mechanism 130 may allow the
armature pin 124 to travel beyond its positions effected by the
electrical actuator 128 so that the armature pin 124 does not limit
movement of the valve member 126. Although a particular embodiment is
shown, it should be appreciated that alternative overtravel mechanisms
may be used with pressure relief valve 120, or alternative pressure
relief valves. For example, as shown in FIG. 7, a two-stage pressure
relief valve 140 may include an overtravel mechanism 142 that includes an
armature pin coupling spring 144 and, as shown, does not require a spring
bore within solenoid 146. Pressure relief valve 140, which is similar to
pressure relief valve 120 of FIG. 6, may also include a solenoid preload
spring 148 for biasing armature pin 150 toward valve member 152.

[0031]According to yet another alternative embodiment, shown in FIG. 8,
the pressure relief subsystem 52 may include a two-stage pressure relief
valve 160 that operates similarly to a fuel injector. Unlike a fuel
injector check valve, however, a check valve 162 of the two-stage
pressure relief valve 160 may open into a drain line, such as the drain
lines 45 shown in FIG. 1, rather than into a cylinder. Specifically, upon
actuation of the check valve 162, such as by energizing an electrical
actuator 164, a fluid connection between the common rail 34 and tank 28
may be opened to selectively relieve pressure within the common rail 34.
In addition, sufficiently high pressure below a small pilot valve 166 may
cause the valve 166 to open and, thus, drain fuel without actuation of
the electrical actuator 164.

[0032]It should also be appreciated that actuation of the electrical
actuator 80 may be controlled via control signals communicated from the
electronic controller 48. Such control signals may be generated
responsive to conditions of the low static leak fuel system 26 and/or the
engine system 10. For example, control signals may be communicated to the
two-stage pressure relief valve 54 in response to sensors or load
determinations. For example, a pressure sensor (not shown) may be
configured to sense a pressure of fuel within the common rail 34. In
addition, sensors may be configured to sense one or more different or
additional parameters of the fuel, such as, for example, temperature,
viscosity, flow rate, or any other parameter known in the an. Sensors, or
other devices, may similarly be provided to detect conditions or
parameters of the engine system 10. Such information may be communicated
to the electronic controller 48 and used to monitor and/or control
operation of the engine system 10 and/or low static leak fuel system 26.

[0033]Referring generally to the graphs of FIGS. 9a-9d, and also
referencing FIGS. 1-4, an exemplary operation of the engine system 10
with respect to key pressures and operation of the two-stage pressure
relief valve 54 is shown. At time t1, a starting process of the
internal combustion engine 12 may be initiated using known starting
means. As shown in FIG. 9d, it may be desirable to increase, and
maintain, a current rail pressure 180 at or near a desired rail pressure
182 during the starting process, and throughout operation of the internal
combustion engine 12. For example, at time t1, the two-stage
pressure relief valve 54 may be moved to the first configuration, shown
in FIG. 2, by energizing the electrical actuator 80, as reflected in FIG.
9a. By moving the valve member 78 to close valve seat 72, as shown in
FIG. 9b and described above, rail pressure may be effectively sealed from
the drain, or fuel tank 28, thus allowing the current rail pressure 180
to increase toward the desired rail pressure 182.

[0034]As current rail pressure 180 quickly approaches the desired rail
pressure 182 near time t2, the two-stage pressure relief valve 54
may be moved into the second configuration of FIG. 3 to "leak" and, as a
result, dampen an overshoot. For example, the electronic controller 48
may communicate a pressure overshoot control signal to the electrical
actuator 80 to move the valve member 78 from the first position to the
second position, and then back to the first position, in response to an
engine load increase determination. Specifically, the electrical actuator
80 may be briefly de-energized, thus allowing the valve member 78 to move
out of contact with the valve seat 72 using the spring force of weak
spring 88 or an opening force acting on the opening hydraulic surface 90
of the valve member 78. While briefly in a slightly opened position, the
two-stage pressure relief valve 54 may open a small flow area fluid
connection between the common rail 34 and the fuel tank 28, as
illustrated in the graph of FIG. 9c, to reduce rail pressure. According
to the alternative two-stage pressure relief valve 120 of FIG. 6, a
similar movement of valve member 126 may be effected by energizing the
electrical actuator 128 to move the valve member 126 to a slightly opened
position, and then de-energizing the electrical actuator 128 to allow
spring 122 to bias the valve member 126 to a closed position.

[0035]Between times t3 and t6, the internal combustion engine 12
may transition from a high load condition to a low load condition. When
this occurs, as shown at time t4, the desired rail pressure 182 may
drop well below the current rail pressure 180. To more quickly reduce the
current rail pressure 180, the electronic controller 48 may communicate a
pressure decay control signal, or parasitic loss control signal, to the
electrical actuator 80 to move the valve member 78 from the first
position to the second position, and then back to the first position, in
response to the engine load reduction determination. As described above,
when the electrical actuator 80 is briefly de-energized, the two-stage
pressure relief valve 54 may fluidly connect the common rail 34 and fuel
tank 28 via a small flow area to reduce the current rail pressure 180.
According to the alternative embodiment of FIG. 6, the current rail
pressure 180 may be reduced by energizing the electrical actuator 128 to
open a small flow area fluid connection, and then de-energizing the
electrical actuator 128 to close the fluid connection.

[0036]As shown near time t5, current rail pressure 180 may increase
above a predetermined maximum operating pressure 184 in the common rail
34. Such a gross over-pressurization may occur due to one or more of an
operational, control, or component issue. To protect the low static leak
fuel system 26 from damage, in such an over-pressurized state, the
two-stage pressure relief valve 54 may be moved to the third
configuration of FIG. 4, as reflected in graphs 9a-9d. Particularly, the
increase in current rail pressure 180 may be sufficient to urge the valve
member 78 out of contact with the valve seat 72, and into the third
position, against the predetermined pre-load of strong spring 92. As a
result, a large flow area through the two-stage pressure relief valve 54
may be opened to reduce pressure in the common rail 34 below the
predetermined maximum operating pressure 184.

[0037]The large flow area, as should be appreciated, may be greater than
the flow area opened in the second configuration of the two-stage
pressure relief valve 54. Precise dimensions of both flow areas, as
should be appreciated, may be selected based on desired performance of
the two-stage pressure relief valve 54. For example, if the small flow
area is too large, the valve 54 may not provide the desired rail pressure
control. If, however, the small flow area is too small, the valve 54 may
not provide the ability to precisely control rail pressure within desired
times. Alternatively, the large flow area may be configured to quickly
dump rail pressure, rather than provide a more controlled leakage.

[0038]At time t6, the internal combustion engine 12 may be shut down,
thus reducing the desired rail pressure 182, as shown. To relieve rail
pressure from the low static leak fuel system 26 when the internal
combustion engine 12 is shut down, the electronic controller 48 may
communicate a depressurization control signal to the electrical actuator
80 to move the valve member 78 from the first position to the second
position in response to an engine off determination. As a result, the
two-stage pressure relief valve 54 may be opened to drain pressure from
the fuel system 26 toward a predetermined minimum operating pressure 186.
By relieving the low static leak fuel system 26 of the current pressure,
maintenance or repair of the fuel system 26, when the internal combustion
engine 12 is off, may be more safely performed.

[0039]Although the pressure relief subsystem 52 is exemplified as
including the two-stage pressure relief valve 54 (or valves 100, 120,
140, or 160), it should be appreciated that the functions described
herein with respect to the two-stage pressure relief valve 54 may be
performed using two or more pressure control components. For example, the
pressure relief subsystem 52 may include a first valve that may be
configured to provide pressure relief to reduce over-pressurization in
the fuel system 26, such as by opening the first valve in response to
rail pressure exceeding a maximum operating pressure. The pressure relief
subsystem 52 may also include a second valve, which may be electronically
controlled to vent rail pressure at certain desired times, such as in
some of the situations described above, to assist in rail pressure
control. Specifically, the second valve may provide fast action and
precise operation to allow development and exploitation of comprehensive
fuel control algorithms, particularly for use with low static leak fuel
system 26. For example, by monitoring rail pressure, engine conditions,
and other parameters, such an electronically controlled pressure relief
device may be used to more quickly and precisely synchronize the current
rail pressure 180 with the desired rail pressure 182.

[0041]Referring generally to FIGS. 1-9, an engine system 10 may include an
internal combustion engine 12 having an engine block 14 that defines a
plurality of cylinders 16. A piston 20 is slidable within each cylinder
16 and connected to a crankshaft 22, such that linear movement of the
piston 20 results in rotation of the crankshaft 22, while rotational
movement of the crankshaft 22 results in linear sliding motion of the
pistons 20. The engine system 10 may also include a low static leak fuel
system 26 for supplying fuel into each cylinder 16 at desired times such
that the injected fuel and compressed air are ignited to produce
mechanical energy. However, the engine 12 need not necessarily be a
compression ignition engine as illustrated. The low static leak fuel
system 26 may include a fuel tank 28 configured to hold a supply of fuel,
and a fuel pumping arrangement 30 configured to pressurize the fuel and
direct the pressurized fuel to a plurality of fuel injectors 32 by way of
a common rail 34. A control system 46 may be associated with low static
leak fuel system 26 and/or engine system 10 to monitor and control the
operations of the fuel pumping arrangement 30, fuel injectors 32, and
various other components of the fuel system 26.

[0042]The low static leak fuel system 26 may provide minimal leakage and,
as a result, may improve the overall efficiency, reliability, and
durability of the common rail fuel system 26. However, the lack of static
leakage may present a previously unrecognized performance challenge, such
that when a reduction in rail pressure is required, the pressure may not
be reduced at a desired rate. More specifically, conventionally designed
fuel systems, which allow a tolerable amount of leakage, may increase a
reduction rate, or decay rate, of pressure within the rail, whereas the
low static leak fuel system 26 may not. As a result, for example, the
settle time required for an operational engine utilizing low static leak
fuel system 26 to go from a high load condition, during which relatively
high rail pressures are used, to a low load or idle condition, during
which relatively low rail pressures are used, may be compromised.

[0043]The pressure relief subsystem 52 described herein, which may include
a two-stage pressure relief valve 54, may provide passive pressure relief
to protect common rail fuel system 26 from over-pressurization, and/or
may provide an electrical actuation strategy and means for selectively
venting rail pressure at certain desired times to assist in rail pressure
control. For example, to protect the low static leak fuel system 26 from
damage, in an over-pressurized state, the two-stage pressure relief valve
54 may be moved to an opened configuration, as shown in FIG. 4.
Particularly, the increased rail pressure may be sufficient to urge a
valve member 78 of the two-stage pressure relief valve 54 out of contact
with the valve seat 72 against a pre-load of strong spring 92, thus
fluidly connecting the common rail 34 with the fuel tank 28, or other
drain. As a result, a large flow area through the two-stage pressure
relief valve 54 may be opened to reduce pressure in the common rail 34
below a predetermined maximum operating pressure 184.

[0044]Further, during operation of the engine system 10, the internal
combustion engine 12 may be transitioned from a first high engine load to
a first low engine load. In response, a fluid connection between the
common rail 34 and fuel tank 28 may be briefly opened and then closed.
Specifically, to more quickly reduce the current rail pressure 180, the
electronic controller 48 may communicate a pressure decay control signal,
or parasitic loss control signal, to the electrical actuator 80 to move
the valve member 78 from the first position to the second position, and
then back to the first position, in response to the engine load reduction
determination. When the electrical actuator 80 is de-energized, the
two-stage pressure relief valve 54 may fluidly connect the common rail 34
and fuel tank 28 via a small flow area to reduce the current rail
pressure 180. In addition, when the internal combustion engine 12 is
stopped, the fluid connection between the common rail 34 and fuel tank 28
may be opened and then closed to relieve pressure within the low static
leak fuel system 26.

[0045]Also, during operation, the internal combustion engine 12 may be
transitioned from a second low engine load to a second high engine load.
In response, the fluid connection between the common rail 34 and fuel
tank 28 may be briefly opened and then closed, such as by energizing and
then de-energizing the electrical actuator 80, as described above, to
dampen an overshoot. Although only a few examples have been provided, it
should be appreciated that the pressure relief subsystem 52, which may or
may not include a passive over-pressurization relief aspect, may provide
control of rail pressure within the low static leak fuel system 26
throughout operation of the internal combustion engine 12. Such precise
control may reduce settle times in a variety of operational transitions,
such as those described above.

[0046]In addition, such a pressure relief subsystem 52 may provide desired
"limp home" capabilities. For example, the two-stage pressure relief
valve 54, which, when de-energized, may include a biased open position,
may maintain a desired reduced rail pressure for operating under such
"limp home" conditions. In addition, alternative pressure relief valve
120, which may be biased to a closed position, may facilitate suitable
rail pressure for "limp home" conditions. Of course, in such conditions,
it is assumed that suitable control of the fuel pumping arrangement 30
and fuel injectors 32 is maintained.

[0047]Further, the pressure relief subsystem 52 may be used to reduce
torque reversals, and resulting noise, in a gear train 42 powering the
variable delivery high-pressure pump 40. Specifically, when operating the
internal combustion engine 12 at an idle condition, the variable delivery
high-pressure pump 40 may be required to provide a limited amount of
fuel. In some circumstances, this may require non-pumping movement of the
one or more pistons of the variable delivery high-pressure pump 40.
Shortly thereafter, when pumping resumes, torque reversal may result.
Such torque reversals may be reduced by pumping fuel to the common rail
34 in excess of a combined fuel injection quantity of the plurality of
fuel injectors 32, thus allowing at least one piston to continue pumping.
The excess fuel may be returned to the fuel tank 28 by opening the fluid
connection between the common rail 34 and the fuel tank 28. As should be
appreciated, such control may only be necessary when a low, or minimum,
operating pressure is required.

[0048]It should be understood that the above description is intended for
illustrative purposes only, and is not intended to limit the scope of the
present disclosure in any way. Thus, those skilled in the art will
appreciate that other aspects of the disclosure can be obtained from a
study of the drawings, the disclosure and the appended claims.